Laser assisted molecular beam deposition of thin films for gate dielectrics applications

High dielectric constant (k), the thermal stability and the chemical stability with respect to reaction with silicon of hafnium oxide (HfO ₂), and zirconium oxide (ZrO₂) places them among the leading candidates for an alternative gate dielectric material. High dielectric constant HfO₂ and ZrO₂ thin films have successfully been deposited on silicon substrates at a temperature of 27°C by Laser Assisted Molecular Beam Deposition (LAMED). The LAMBD process is related to conventional Pulsed Laser Deposition (PLD). In the PLD process, the ablation plume impinges directly upon the substrate to deposit the thin film, whereas in the LAMBD process, the ablation material is expanded within a concurrently pulsed stream of a reactive gas. The gas pulse serves both to create the desired material and to transport the material to the substrate for deposition of the thin film. One advantage of the LAMBD process is that a chemically reactive carrier gas can be selected to produce the desired chemical products. Depositions yielded 35 nm to 135 nm thick HfO₂, and ZrO₂ films. Structural and chemical characterization of the films were performed by Auger electron spectroscopy (AES), Rutherford back-scattering (RBS), scanning electron microscopy (SEM), and x-ray diffraction (XRD). Film surface was investigated by atomic force microscopy (AFM) while optical characterization was also performed by means of spectroscopic ellipsometry (SE). Within the process window investigated, the film Hf/O and Zr/O ratios was found to be in the range 0.6 to 1.2. The as deposited films were amorphous with refraction index (RI) at 623 nm wavelength films in the range of 1.22 to 1.27 for the HfO₂ and in the range of 1.23 to 1.19 for the ZrO₂ films.